1. Technical Field
The present invention relates to an ultrasonic sensor for transmitting ultrasonic waves, a tactile sensor for detecting contact with a contact object through the ultrasonic waves transmitted from the ultrasonic sensor, and a grasping apparatus comprising the tactile sensor.
2. Related Art
In conventional practice, there are known sensors for detecting the stress applied by contact with an object when an object of unknown weight and friction coefficient is grasped by a robot arm or the like (see Japanese Laid-Open Patent Publication No. 2006-208248, for example).
The tactile sensor disclosed in Japanese Laid-Open Patent Publication No. 2006-208248 has a structural body with a cantilever structure which extends from the edge of an opening formed in a sensor substrate, and this structural body is configured from a flat plate-shaped sensitive part, and a hinge part which joins the sensitive part and the sensor substrate together. An electroconductive magnetic film is formed on the sensitive part of this structural body, a piezoresistive film is formed on the hinge part, and there is an electrical connection between the electroconductive magnetic film and the piezoresistive film. In this configuration, an electrode is provided to the hinge part and the hinge part folds under pressure, whereby an electrical current generated by the piezoresistance of the hinge part flows from the electrode. In this tactile sensor, a plurality of structural bodies such as the one described above are formed on the sensor substrate, and some of these structural bodies stand upright on the sensor substrate while others are held parallel to the sensor substrate. An elastic boy is provided on the sensor substrate, and the upright structural bodies are embedded in the elastic body. Shearing force can be measured by the upright structural bodies, and positive pressure force can be measured by the structural bodies that are parallel to the substrate surface. In this tactile sensor, shearing force is detected by the structural bodies that stand upright relative to the sensor substrate, and positive pressure force is detected by the structural bodies that are held parallel to the sensor substrate. The upright structural bodies are formed by bending flat plate-shaped structural bodies by magnetism.